Timepiece of this type are known in the prior art. The days of the month 1 to 31 are inscribed on the calendar ring and appear one after the other through an opening cut in the dial. Numerous and varied means have been conceived for driving this ring from the timepiece drive motor. A known type of arrangement will appear in the text of the present description.
In antique watches or in specially constructed timepieces the date does not appear in the form of numbers through an opening but is displayed by means of a hand which is displaced over a dial on which are placed the indications relative to the date. This hand is either coaxial with the hands indicating hours and minutes or displaced from the center of the watch to sweep a small dial graduated according to the date.
An example of this second type of arrangement is described in the Swiss Pat. No. 100 231 where the cannon wheel bears a flexible finger which drives a gear arrangement through one tooth space at each revolution of the cannon wheel which rotates once every twelve hours. The gear arrangement meshes in turn with a calendar wheel which makes one revolution in 24 hours. The date hand is solidly mounted on the calendar wheel by means of a cannon tube. The setting of the date hand is obtained by acting directly on the calendar wheel.
It will be understood that such a mechanism is not adapted to modern watches having a greatly reduced thickness in which it is desired to arrange a date display by means of a hand as dictated by certain current fashions. Above all, such a mechanism requires the reconsideration of the entire construction of known movements which comprise for the most part calendars with a dial opening and which exhibit such greatly reduced thickness.